Magnetic media normally comprise a layer of synthetic resin pigmented with a magnetizable pigment which is carried by a non-magnetic support, typically a layer of ethylene glycol terephthalate polyester, such as is available in commerce under the trade designation Mylar. Because of the speed of production and the achievement of favorable properties, it has been desired to employ radiation-curable compositions, the radiation of preference being electron beam. It is desired to provide electron beam-curable polymers which are hard and tough, especially to blend with the generally softer radiation-curable ethylenically unsaturated polyurethanes which are now available.
At the present time, these generally softer radiation-curable ethylenically unsaturated polyurethanes are blended with polyethylenically unsaturated crosslinking monomers, illustrated by trimethylol propane triacrylate, in order to increase the hardness of the cured composition. Unfortunately, the increased hardness conferred by the polyethylenic crosslinking monomer is obtained at the sacrifice of desired toughness and attendant elongation. It is therefore necessary to develop ethylenically unsaturated polymers which will provide the needed hardness and toughness and to find ways to practically produce such polymers.